STRUCTURE, CONFORMATION, AND THERMOCHEMISTRY OF DIMESITYL METHANETHIAL S-OXIDE (DIMESITYL SULFINE)

The structure of dimesityl sulfine in solution and in the solid state was determined by NMR spectroscopy and X-ray crystallography, respecti vely. In the crystal the two mesityl groups are twisted by approximate ly 60 degrees, while in solution an averaged conformation with C-s sym metry is observed, with the anti mesityl ring located in the C=S=O pla ne and the syn mesityl ring perpendicular to the C=S=O plane, From the coalescence temperature T-c at 303 K, the free energy of activation f or the rotation of the mesityl rings was estimated to be 14 +/- 0.7 kc al/mol. At higher temperatures (140-185 degrees C) dimesityl sulfine y ields up to 95% 5,7-dimethyl-1-mesityl-benzo[c]thiophene.